[Xen-devel] [PATCH 1/6] xen-gntdev: Change page limit to be global instead of per-open

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

Because there is no limitation on how many times a user can open a
given device file, an per-file-description limit on the number of
pages granted offers little to no benefit. Change to a global limit
and remove the ioctl() as the parameter can now be changed via sysfs.

Xen tools changeset 22768:f8d801e5573e is needed to eliminate the
error this change produces in xc_gnttab_set_max_grants.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 drivers/xen/gntdev.c |   50 ++++++++++++++------------------------------------
 1 files changed, 14 insertions(+), 36 deletions(-)

diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
index 2b777c0..3ca47d1 100644
--- a/drivers/xen/gntdev.c
+++ b/drivers/xen/gntdev.c
@@ -45,15 +45,15 @@ MODULE_AUTHOR("Derek G. Murray <Derek.Murray@xxxxxxxxxxxx>, 
"
              "Gerd Hoffmann <kraxel@xxxxxxxxxx>");
 MODULE_DESCRIPTION("User-space granted page access driver");
 
-static int limit = 1024;
+static int limit = 1024*1024;
 module_param(limit, int, 0644);
-MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped at "
-               "once by a gntdev instance");
+MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped by "
+               "the gntdev device");
+
+static atomic_t pages_mapped = ATOMIC_INIT(0);
 
 struct gntdev_priv {
        struct list_head maps;
-       uint32_t used;
-       uint32_t limit;
        /* lock protects maps from concurrent changes */
        spinlock_t lock;
        struct mm_struct *mm;
@@ -82,9 +82,7 @@ static void gntdev_print_maps(struct gntdev_priv *priv,
 #ifdef DEBUG
        struct grant_map *map;
 
-       pr_debug("maps list (priv %p, usage %d/%d)\n",
-              priv, priv->used, priv->limit);
-
+       pr_debug("%s: maps list (priv %p)\n", __func__, priv);
        list_for_each_entry(map, &priv->maps, next)
                pr_debug("  index %2d, count %2d %s\n",
                       map->index, map->count,
@@ -121,9 +119,6 @@ static struct grant_map *gntdev_alloc_map(struct 
gntdev_priv *priv, int count)
        add->count = count;
        add->priv  = priv;
 
-       if (add->count + priv->used > priv->limit)
-               goto err;
-
        return add;
 
 err:
@@ -154,7 +149,6 @@ static void gntdev_add_map(struct gntdev_priv *priv, struct 
grant_map *add)
        list_add_tail(&add->next, &priv->maps);
 
 done:
-       priv->used += add->count;
        gntdev_print_maps(priv, "[new]", add->index);
 }
 
@@ -200,7 +194,7 @@ static int gntdev_del_map(struct grant_map *map)
                if (map->unmap_ops[i].handle)
                        return -EBUSY;
 
-       map->priv->used -= map->count;
+       atomic_sub(map->count, &pages_mapped);
        list_del(&map->next);
        return 0;
 }
@@ -385,7 +379,6 @@ static int gntdev_open(struct inode *inode, struct file 
*flip)
 
        INIT_LIST_HEAD(&priv->maps);
        spin_lock_init(&priv->lock);
-       priv->limit = limit;
 
        priv->mm = get_task_mm(current);
        if (!priv->mm) {
@@ -442,19 +435,24 @@ static long gntdev_ioctl_map_grant_ref(struct gntdev_priv 
*priv,
        pr_debug("priv %p, add %d\n", priv, op.count);
        if (unlikely(op.count <= 0))
                return -EINVAL;
-       if (unlikely(op.count > priv->limit))
-               return -EINVAL;
 
        err = -ENOMEM;
        map = gntdev_alloc_map(priv, op.count);
        if (!map)
                return err;
+
        if (copy_from_user(map->grants, &u->refs,
                           sizeof(map->grants[0]) * op.count) != 0) {
                gntdev_free_map(map);
                return err;
        }
 
+       if (unlikely(atomic_add_return(op.count, &pages_mapped) > limit)) {
+               pr_debug("can't map: over limit\n");
+               gntdev_free_map(map);
+               return err;
+       }
+
        spin_lock(&priv->lock);
        gntdev_add_map(priv, map);
        op.index = map->index << PAGE_SHIFT;
@@ -517,23 +515,6 @@ static long gntdev_ioctl_get_offset_for_vaddr(struct 
gntdev_priv *priv,
        return 0;
 }
 
-static long gntdev_ioctl_set_max_grants(struct gntdev_priv *priv,
-                                       struct ioctl_gntdev_set_max_grants 
__user *u)
-{
-       struct ioctl_gntdev_set_max_grants op;
-
-       if (copy_from_user(&op, u, sizeof(op)) != 0)
-               return -EFAULT;
-       pr_debug("priv %p, limit %d\n", priv, op.count);
-       if (op.count > limit)
-               return -E2BIG;
-
-       spin_lock(&priv->lock);
-       priv->limit = op.count;
-       spin_unlock(&priv->lock);
-       return 0;
-}
-
 static long gntdev_ioctl(struct file *flip,
                         unsigned int cmd, unsigned long arg)
 {
@@ -550,9 +531,6 @@ static long gntdev_ioctl(struct file *flip,
        case IOCTL_GNTDEV_GET_OFFSET_FOR_VADDR:
                return gntdev_ioctl_get_offset_for_vaddr(priv, ptr);
 
-       case IOCTL_GNTDEV_SET_MAX_GRANTS:
-               return gntdev_ioctl_set_max_grants(priv, ptr);
-
        default:
                pr_debug("priv %p, unknown cmd %x\n", priv, cmd);
                return -ENOIOCTLCMD;
-- 
1.7.3.4


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